1. Field of the Invention
The present invention relates to external systems for vehicle diagnostics and more particularly to a wireless communication system for vehicle diagnostics equipment.
2. Description of the Prior Art
Contemporary designs for the control and management of vehicle components increasingly rely on methods derived from computer networking. Digital data is exchanged between component controllers over a common physical layer, such as a twisted shielded pair of wires. Intelligible communication between two or more device controllers among a greater plurality of devices, all occurring over the common physical layer, depends upon the communicating devices being able to discriminate among messages they receive and respond to those messages directed to them. Such methods are well known in the art and are part of the standards which the Society of Automotive Engineers (SAE) has published and continues to publish as part of the SAE J1939, and SAE J1708/1587 protocols. Another pertinent protocol is the Assembly Line Data Link (ALDL) protocol published by General Motors Corp.
These protocols define the performance requirements of the medium of the physical layer, but also allow for development of proprietary protocols. The SAE J1939 protocol is a specialized application of a controlled area network (CAN) and may be readily implemented utilizing commercial integrated circuits such as the C167 Integrated Circuit from Siemens of Germany. The J1708/1587 was R5485. ALDL uses a standard Universal Asynchronous Receiver/Transmit (UART) port.
The CAN protocol is an ISO standard (ISO 11898) for serial data communication, particularly aimed at automotive applications. The CAN standard includes a physical layer (including the data bus) and a data-link layer, which define a few different message types, arbitration rules for bus access and methods for fault detection and fault confinement. The physical layer uses differential transmission on a twisted pair wire bus. A non-destructive bitwise arbitration is used to control access to the bus. Messages are small, at most eight bytes, and are protected by checksum error detection. Each message carries a numeric value which controls its priority on the bus and typically also serves as an identification of the contents of the message. CAN offers an error handling scheme that results in retransmission of messages when they are not properly received. CAN also provides means for removing faulty nodes from the bus. CAN further adds the capability of supporting what are termed xe2x80x9chigher layer protocolsxe2x80x9d for standardizing startup procedures including bit rate setting, distributing addresses among participating nodes or kinds of messages, determining the layout of the messages and routines for error handling on the system level.
Digital data communications over serial data paths are an effective technique for reducing the number of dedicated communication paths between the numerous switches, sensors, devices and gauges installed on the vehicles. Multiplexing the signals to and from local controllers on a bus gives greater physical simplicity through displacing much of the vehicle wiring harness thereby reducing manufacturing costs and enhancing system reliability.
Considering, by way of example, the J1939 standard, diagnostic and programming stations used for performing vehicle, particularly truck, diagnostic routines have routinely communicated with a vehicle""s internal network by an external J1939 linkage. The external linkage comprises a J1939 compatible cable connected between an external, temporarily connected computer and a diagnostic port which is, in turn, on a node of the internal vehicle network. The diagnostic program then runs on the external computer and communicates with the vehicle network over the external linkage.
External J1939 cable linkages and supporting equipment are limited to about 4 meters (13xe2x80x2) in length without the need to introduce line amplifiers. Specifically, the cables from the vehicle diagnostic plug to an interface adaptor are limited to about 1 meter (3xe2x80x2) and the standard recommends a maximum length of only about 46 cm (18xe2x80x2). The serial port cable from the computer to the interface adaptor is allowed to be a maximum of about 2.75 meters (9xe2x80x2). Given an interface adaptor length of about a foot, thirteen feet is the maximum spacing that can be obtained with a physical connection. Since the interface adaptor is required to be connected to the computer serial port, the maximum allowed data rate is 115 kb/s into the computer notwithstanding the fact that the J1939 network can run at 250 kb/s. These interface limitations limit the system to testing one truck at a time and require either that the diagnostic computer be brought into close proximity to the truck being tested or that a number of expensive line amplifiers be used, which slow the process of testing vehicles and add expense.
Wireless communications systems have recently become widespread, but have not been applied to vehicle diagnostics stations. Among the standards for wireless communication are those for wireless local area networks (WLAN), including specifically the 802.15 Standard of the Institute of Electrical and Electronics Engineers (IEEE Stnd. 802.15). The topology of such networks may be ad hoc, that is established temporarily for a particular purpose among nodes or stations which recognized each other and which have established communications.
Three types of network physical layers have been widely used for WLAN: (1) Direct Sequence Spread Spectrum (DSSS) radio; (2) Frequency Hopped Spread Spectrum (FHSS); and (3) Infrared (IR). The IEEE Stnd. 802.15 provides a FHSS physical layer. FHSS exploits the 2.4 GHz Instrumentation, Scientific and Medical microwave band, in which the FCC and numerous international and foreign authorities have allowed unlicensed low power density transmission. At the time that this patent is being written, FHSS physical layers support data transmission speeds up to 1 Mb/s and it is anticipated that data transmission speeds of up to 2 Mb/s will become available without changes to the physical layers. In terms of components, a WLAN may be established by introducing the appropriate cards to computers and attaching the cards to antenna. For example, Ericsson, Inc. Components of Richardson, Texas supplies a radio which may be installed on a PC card which, in turn, plugs into a PCMCIA bus commonly used in portable computers and to which an external antenna may be connected to implement a potential node in a WLAN.
The invention provides an apparatus and a method of evaluating vehicle electrical control systems. In implementing the method of the invention a base evaluation and programming station is provided by an appropriately programmed portable computer. A wireless network communication interface is connected to the base evaluation and programming station. Vehicles may then be brought into the general vicinity of the base station. The electrical control system for each vehicle brought into range for testing may be temporarily attached to a transferable wireless node including a wireless communication interface and two way data staging element. Thereupon an ad hoc network is established with individual communication links between the wireless communication interface connected to the base evaluation and programming station and each transferable wireless communication interface.
Additional effects, features and advantages will be apparent in the written description that follows.